Potential recording marker



June 27, 19440 M. APSTEHN 2,352,242

POTENTIAL RECORDING MARKER Filed Feb. 14, 1941 IN VENTOR.

MW (MW Patented June 27, 1944 POTENTIAL RECORDING MARKER Maurice Apstein, Brooklyn, N. Y. Application February 14, 1941, Serial No. 378,949

4 Claims.

This invention relates to a device for the instantaneous recording upon a movable record receiving surface, the variations of an electric potential with respect to time, and is primarily concerned with an actuating mechanism and an amplifying circuit therefor.

The prior art methods for accomplishing this purpose may be divided roughly into two classes, namely direct and indirect methods. The indirect methods are those which record photographicaliy the deflection of a beam of light and thus entail the inconvenience, expense, delay and uncertainty of photographic technique.

The direct methods usually employ the piezoelectric effect to obtain a deflection of small amplitude which is subsequently amplified by a system of mechanical levers. Due to the variation in sensitivity, with respect to temperature and the minute original deflections of piezoelectric material available for this purpose, such technique results in considerable instability of operation and a mechanism in which an extremely high degree of precision is required, if satisfactory operation is to be obtained.

One object of the present invention is to provide a driving mechanism for such an aforementioned device which is substantially independent of variations in temperature and humidity.

A further object is to provide a mechanism in which the initial deflection is sufliciently large, so that further mechanical amplification is either unnecessary or reduced to a minimum, thus reducing the necessity for a high degree of precision in manufacture and consequently reducing the cost of manufacture, at the same time that ruggedness, dependability and accuracy are increased.

A further object is to provide a mechanism in which the original motion imparted is an angular displacement of a shaft.

A further object of this invention is to provide a driving mechanism so constructed that it may be connected to a vacuum tube amplifier in such manner that the undesirable effects of mechanical resonance in said driving mechanisms are largely suppressed.

The actuating force of the driving mechanism associated with the present invention is magnetomotive. Prior art magnetomotive mechanisms have been either of the moving conductor or balanced armature type. The moving conductor mechanism has the advantage of large inherent amplitude capability, but the disadvantage that a coil of suitably small mass presents too low an impedance to be efliciently coupled directly to a vacuum tube amplifier.

If such a mechanism is connected to an amplifier, through a transformer, then the low frequency limit of the transformer response determines the low frequency response of the entire instrument. Since the potentials which recording markers of .this type are usually required to reproduce contain components as low as one or two cycles per second as well as direct current, such transformer coupling is impracticable. The balanced armature type of mechanism, like the piezo-electric type, is characterized by a small initial amplitude and thus necessitates a large mechanical lever system for amplification with all the inherent disadvantages thereof.

- present invention, comprises a magneto-motive The driving mechanism associated with the mechanism capable of sufllciently large initial amplitudes to require little or no mechanical amplification and at the same time presents "a sufllciently high impedance so that it may be efiiciently coupled directly to a vacuum tube amplifier.

A description of the driving mechanism, the preferred method of coupling to a vacuum tube amplifier and means for transferring oscillatory displacements of the driving mechanism to a moving marking surface, may be clearly understood by reference to the accompanying drawing in which:

Fig. 1 shows a perspective view of the driving mechanism and the preferred method of connection to a vacuum tube amplifier.

Fig. 2 is a side view of the disposition of the essential mechanical elements of the invention and shows means by which oscillatory deflections of the driving mechanism are translated into an oscillographic marking upon a moving marking surface. A source of steady magnetic flux is shown as a permanent horse-shoe type magnet I, with the poles of which are associated four soft iron, high permeability pole pieces 2, 3, 4, 5. Surrounding each pole piece is its associated actuating coil 6, 1, 8,18, shown for simplicity as a few turns of wire each, although in practice, the number of turns is determined by the characteristics of the amplifier from which the coils are excited.

In the two magnetic gaps thus formed, two highly permeable armatures l0 and H are mounted in spaced relation on a shaft l2, journalled in bearings (not shown) so that it may be angularly displaced about its axis, but is incapable of other movement. The armatures l0 and II are elongated rectangles in plan, so mounted that the planes formed by their longitudinal axes and the axis of the shaft are at an angle to each other. The degree of this angle determines the maximum angular deflection of the shaft during operation; an angle of approximately sixty degrees has been found satisfactory for present purposes. The faces of the pole pieces 2, I, I, I are so proportioned that their dimensions are approximately equal to the dimensions of the ends of the armatures II and I l which are spaced in conformity.

Operation is as follows: With no potential applied io the coils, the flux in the gaps tends to draw both armatures wholly into the gaps, resulting in a clockwise torque on the upper armature Ill and an equal counterclockwise torque on the lower armature H. The result is that the shaft takes a position of equilibrium, such that each armature is halfway in and halfway out of its respective gap.

Coils I and 8 are connected in series. Coils I and 9 are also connected in series and polarized so that when potential is applied, current flows through the coils creating a magnetic flux in each coil. The magnetic flux in the coils surrounding the upper opposed pair of pole pieces is in opposition to the steady flux from the permanent magnet I at the same time that the magnetic flux in the coils surrounding the lower opposed pair of pole pieces is in the same direction as the flux from the permanent magnet. This condition results in an inequality in magnetic flux such that the flux in one gap is increased, while a corresponding decrease takes place in the other gap. This inequality in magnetic flux causes an angular displacement of the shaft to a new position, such displacement being either clockwise or counterclockwise, depending upon the polarity of the applied potential.

as shown in Figure 1, when grid I1 is positive and grid l8 negative during reception of a signal current will flow from battery (positive terminal) I! through parallel paths including (1) winding 9, anode l3, cathode l8 and winding 8 and then back to negative terminal of battery It; and (2) winding I, anode ll, cathode II, and winding 8 and then back to negative of battery It. i

If an alternating potential is applied, the shaft will oscillate back and forth at a frequency equal to the frequency of the alternating potential and at an amplitude proportional to its magnitude.

The frequency response of the device described is essentially uniform up to the first mechanical resonant frequency, this frequency being determined by magnetic restoring force, and the mass of the moving system. As the resonance frequency is approached, the response increases due to resonance and subsequently falls below normal after resonance is passed. The method of con nection to a vacuum tube amplifier described below tends to overcome this resonant rise in response and results in an essentially uniform sensitivity to all frequencies up to, including and slightly higher than the first resonant frequency. Referring again to Figure 1, A, B, C, D, E, G, H designate the several terminals of the four actuating coils. 33 and 34 designate two vacuum tubes of a push-pull amplifier stage which may be the last stage in a multi-stage amplifier. II and il designate the anodes, l6 and ii designate the cathodes, and I1 and it designate the control grids of these vacuum tubes. Eu. de-

notes the signal source or potential which it is desired to record. ll refers to a source of anode potential and 2. refers to negative bias source for the rid circuit. both sources shown as batteries. 2|, 22 indicate 811d resistors to provide a return path from mid to cathode. The tubes II and It as shown are of the indirectly heated cathode type and the heater circuit is not shown for simplicity. To any one familiar with the art it should be obvious that filament type tubes may be used if desired. In addition, although the tubes shown are triodes, tetrodes or pentodes may be substituted if desired.

It will be noted that the coils i and I are in series with the cathodes of th tubes and thus are common to the plate-cathode and grid-cathode circuits of their respective tubes. The effect of such common connection is to reduce the effective amplification at resonance, resulting in a corresponding reduction in displacement at resonance and a consequent flattening of the response curve.

Figure 2 is a side view of the disposition of the essential mechanical elements of the invention, by means of which angular displacements of the shaft i2 are translated directly into an oscillographic marking upon a moving marking surface shown as a paper tape 21. l, 2. 3, and i2 designate the magnet, pole pieces, and shaft, respectively. shown in detail in Figure 1. A hub 23 is firmly afllxed to the shaft II, by means of set screw 2i. A thin tube 2! passes through the hub 23 and connects to a small flexible hose 2!, which serves to carry ink from a reservoir (not shown) to the extremity 32, of the tube 25, this extremity acting as a pen point for marking.

A paper tape 21, stored in a roll, is free to rotate around the shaft 29 with sufllcient friction to keep the tape 21 flat and taut.

The tape 21 passes over a flat plate 28, so disposed as to be adjustable with the pen point 12. The adjustable means are not shown. With proper ink flow from the tube 26, a small drop of ink forms at its extremity 32. When spacing between the plate 28 and pen point 32 is made slightly less than the radius of the drop of ink and when the plane of the plate 28 and the plane of the are described by the moving pen point 32 are parallel, marking will occur on the moving tape 21 with negligible friction since the pen point 32 and the paper tape 21 are not in actual contact.

A motor driven friction pulley II serves to pull the tape 21 over the plate 28. An idlin roller 3| serves to keep the tape 21 in contact with the pulley 30 without slippage. By the operation described, direct recording of varying potentials applied to the instrument may thus be obtained on the moving tape.

I claim:

l. A potential measuring device comprising, in combination, a magneto-motive driving mechanism including a horseshoe magnet, pairs of pole pieces mounted in spaced-apart relation on each pole of said magnet, two opposing pole pieces being arranged in one plane and the other two opposing pole pieces being arranged in a parallel plane, said opposing pole pieces having gaps between them, a shaft mounted for oscillatory movement intermediate said pole pieces, a pair of permeable armatures mounted on said shaft, said armatures being in relative angular relation with each other, said armatures being positioned in said gaps between said opposing pairs of pole pieces and lying in said parallel planes, each pole piece having an enclosing actuating coil, the

coils on one side of said shaft being interconnected in series, the coils on the other side of said shaft being interconnected in series, vacuum tube amplifiers, a source of electric energy connected with said amplifier tubes, said pairs of coils in series being connected with the output circuits of their respective amplifiers, a biasing battery connected with each of said amplifier tubes to control the current flow in said amplifier tubes, a pair of resistors in said respective grid circuits of said amplifier tube's, whereby a potential applied .to said grid circuits causes a change in the current fiow of said tubes, said current causing a decrease in the magnetic flux in one of said opposed pairs of pole pieces and a corresponding increase in the magnetic flux in the other opposed pair of pole pieces, said change in the magnetic flux resulting in a strengthening of the torque on one armature and a weakening of the torque on the other armature during one-half of the input alternating current cycle and vice versa during the other half of said cycle. 2. In a potential measuring device, comprising a magneto-motive driving mechanism including a source of steady magnetic flux, pairs of pole pieces mounted in spaced-apart relation on each pole of said magnet, two opposing pole pieces being arranged in one plane and the other two opposing pole pieces being arranged in a parallel.

plane, said opposing pole pieces having gaps between them, a shaft mounted for oscillatory movement intermediate said pole pieces, said shaft having two permeable rectangular armatures mounted thereon, said armatures having their major axes in angular relation with each other and in intersecting relation with the axis of said shaft, said armatures being positioned in said gaps between said opposing pairs of pole pieces and lying in said parallel planes, each pole piece.

having an enclosing actuating coil, the coils on one side of said shaft being interconnected in series, the coils on the other side of said shaft being interconnected in series, vacuum tube amplifiers, a source of electric energy connected with said amplifier tubes, said pairs of coils in series being connected with the output circuits of their respective amplifiers, a biasing battery connected wth each of said amplifier tubes to control the current flow in said amplifier tubes, a pair of resistors in said respective grid circuits of said amplifier tubes, whereby a potential applied to said grid circuits causes a change in the current fiow of said tubes, said current causing a decrease in the magnetic fiux in one of said opposed pairs of pole pieces and a corresponding increase in the magnetic flux in the other opposed pair of pole pieces, said change in the magnetic flux resulting in a strengthening of the torque on one armature to turn it in" one direction and a weakening of the torque on the other armature during one-half of the input alternati'ng current cycle and vice versa during the other half of said cycle.

3. A potential measuring device comprising in combination with vacuum tube amplifiers, a

source of steady magnetic flux, permeable pole pieces fixed in pairs and in spaced-apart relation on each pole of said magnet, two opposing pole pieces arranged in one plane and the other two opposing pole pieces being arranged in a parallel plane, said opposing pole pieces having gaps v between them, a shaft mounted .for oscillatory movement intermediate said pole pieces, said posing pairs of pole pieces and lying in said parallel planes, each pole piece having an enclosing actuating coil, the coils on one side of said shaft being interconnected in series, the coils on the other side of said shaft being interconnected in series, a source of electric energy connected with said amplifier tubes, said pairs of coils in series being connected with the output circuits of their v respective amplifiers, a biasing battery connected with each of said amplifier tubes to control the current flow in said amplifier tubes, a pair of resistors in said respective grid circuits of said amplifier tubes, whereby a potential applied to the input of said amplifiers causes a change in the current flow of said tubes, said current causing a decrease in the magnetic flux in one of said opposed pairs of pole pieces and a corresponding increase in the magnetic flux in the other opposed pair of pole pieces, said change in the magnetic flux resulting in a strengthening of the torque on one armature to turn it in one direction and a weakening of the torque on the other armature during one-half of the input alternating current cycle and vice versa during the other half of said cycle.

4. In a potential measuring device, comprising in combination with vacuum tube amplifiers a magneto-motive driving mechanism comprising a steady source of magnetic flux, permeable pole pieces fixed in pairs and in spaced-apart relation on each pole of said magnet, two opposing pole pieces being arranged in one plane and the other two opposing pole pieces being arranged in a parallel plane, said opposing pole pieces having gaps between them, a shaft mounted for oscillatory movement intermediate said pole pieces, a plurality of armature segments mounted on said shaft, said armature segments being positioned in said gaps between said opposing pairs of pole pieces and lying in said parallel planes, each pole piece having an enclosing actuating coil, the coils on one side of said shaft being interconnected in series, the coils on the other side of said shaft being interconnected in series, a source of electric energy connected with said amplifier tubes, said pairs of coils in series being connected with the output circuits of their respectiv amplifiers, a biasing battery connected with each of said amplifier tubes to control the current fiow in said amplifier tubes, a pair of resistors in said respective grid circuits of said amplifier tubes, whereby a potential applied to the grids of said amplifiers causes a change inthe current fiow of said tubes, said current causing a decrease in the magnetic flux in one of said opposed pairs of pole pieces and a corresponding increase in the magnetic flux in the other opposed pair of pole pieces, said change in the magnetic flux resulting in a strengthening of the MAURICE APS'I'EIN. 

